Few days back ars technica found a code of Android N freeform window mode ( Use Actual multiple windows at the same time like remix os ) , but the feature was not there in Android N . But now you can enable this awesome feature if you are using Android N developer preview .
|image via - ars technica|
You can even use freeform window in split screen too , though it will use much RAM and might lag in many devices with low RAM . May be that's the reason Google hid this feature . But you can still enable it by doing a little work .
To enable it follow Ars technica guide .